Downshift inhibitor circuit

Abstract

In a transmission control system for a multiple speed ratio powershift transmission having a plurality of fluid pressure operated clutches adapted to establish torque ratio changes and also including an electronic speed sensing system and downshift valve means for automatically shifting the transmission from a higher speed ratio to a lower speed ratio at a first predetermined vehicle ground speed, the addition of a downshift inhibitor or delay circuit for prohibiting downshifts from the higher speed ratio to the lower speed ratio while the vehicle undergoes a full throttle directional reversal.

What is claimed is: 
     
       1. In a transmission control system for a vehicle including a multiple speed ratio powershift transmission having a plurality of fluid pressure operated clutches, adapted to establish torque ratio changes; a source of pressurized fluid; a speed control cover including a manually-actuated control means and a speed control valve for controlling the flow of fluid to said clutches; an electronic speed sensing system; and downshift valve means, for automatically shifting said transmission from a higher speed ratio to a lower speed ratio at a first predetermined ground speed by diverting the fluid for pressurizing a higher speed ratio clutch to a lower speed ratio clutch and automatically shifting said transmission from said lower speed ratio back to said high speed ratio at a second predetermined ground speed by ceasing the diverting of said fluid, wherein the improvement comprises means for prohibiting automatic downshifts from said higher speed ratio to said lower speed ratio while said vehicle undergoes a rapid directional reversal. 
     
     
       2. The improved transmission control system of claim 1 wherein said means for prohibiting downshifts includes a downshift delay circuit. 
     
     
       3. The improved transmission control system of claim 2 wherein said electronic speed sensing system includes an electronic speed switch and a solenoid valve and said downshift delay circuit is interposed in said electronic speed sensing system between said electronic speed switch and said solenoid valve. 
     
     
       4. The improved transmission control system of claim 3 wherein said downshift delay circuit basically takes the form of a timer circuit including a relay and a timer, with said relay being activated upon the initiation of a vehicle directional reversal while said vehicle travels at said higher speed ratio, with said timer however not starting until said vehicle has attained said first predetermined ground speed. 
     
     
       5. The improved transmission control system of claim 4 wherein said higher speed ratio is second gear and said lower speed ratio is first gear. 
     
     
       6. The improved transmission control system of claim 5 wherein said timer circuit delays the downshift of said transmission for a predetermined length of time which is sufficient for said vehicle to reverse and accelerate, at full throttle, to the normal second gear speed range. 
     
     
       7. The improved transmission control system of claim 6 wherein said predetermined length of time is of sufficient duration that said vehicle is able to go through a normal cycle of slowdown, stop and acceleration in second gear in another direction, until the ground speed thereof exceeds said second predetermined speed, before said predetermined length of time is exceeded. 
     
     
       8. For use with a vehicle having a transmission with separate fluid operated clutches for selecting a plurality of speed ratios as well as forward drive and reverse drive, a transmission control system including a source of pressurized fluid; a transmission control cover with a speed control valve for controlling the flow of fluid to said speed ratio clutches; a transmission automatic downshift system comprising an electronic speed sensing system, including an electronic signal generator, an electronic speed switch and a solenoid valve; said electronic speed sensing system being in combination with downshift valve means for automatically shifting said transmission, while said speed control valve is set for a second speed ratio, to a lower first speed ratio, at a first predetermined ground speed by diverting pressurized fluid from a second speed ratio clutch to a first speed ratio clutch and thereafter, at a second higher predetermined ground speed, automatically shifting back to said second speed ratio by ceasing the diverting of said fluid, wherein the improvement comprises a downshift inhibitor circuit for prohibiting automatic downshifts from said second speed ratio to said first speed ratio while said vehicle undergoes a rapid directional reversal. 
     
     
       9. The improved transmission control system of claim 8 wherein said downshift inhibitor circuit is interposed in said electronic speed sensing system between said electronic speed switch and said solenoid valve, with said downshift inhibitor circuit taking the form of a timer circuit including a relay and a timer, with said relay being activated upon the initiation of a vehicle directional reversal while said vehicle operates in said second speed ratio, with said timer however not starting until said vehicle has attained said first predetermined ground speed. 
     
     
       10. The improved transmission control system of claim 9 wherein said timer circuit delays the downshift of said transmission for a predetermined length of time which is of sufficient duration that said vehicle is able to go through a normal cycle of slowdown, stop and acceleration in said second gear ratio in an opposite direction, until the ground speed thereof exceeds said second higher predetermined ground speed.